The invention described herein was made in the course of, or under, Contract No. W-7405-ENG-48, with the Energy Research and Development Administration.
The invention relates to regeneration of molecular sieve drying beds, and particularly to a regeneration technique using an auxiliary molecular sieve bed whereby the partial pressure of water can be reduced to a very low level.
Molecular sieves (complex aluminum-silicates) are widely used for drying gases. When the drying bed reaches its adsorption capacity, it is regenerated by passing a hot inert gas through the bed to drive off (desorb) the adsorbed water. In these prior systems, a circulating inert gas is heated and passed through the "saturated" molecular sieve bed to desorb the adsorbed water. The moist gas is then cooled below its dew point and passed through a liquid-gas separator. The separated water is drained, and the dry gas phase is recirculated through the system. This prior type of regeneration system is capable of reducing the partial pressure of water (P.sub.w) in the drying bed to about 10.sup.-7 atm., when it is returned to normal service. While this is adequate in most cases, certain critical applications occur where P.sub.w must be maintained at much lower levels. For example, in certain controlled thermonuclear reactor (CTR) applications tritiated water (T.sub.2 O, HTO) must be collected and P.sub.w maintained in the range of 10.sup.-9 atm. This P.sub.w level is a factor of 100 lower than that obtainable with conventional systems for regenerating molecular sieve dryers. Thus, a need exists in the molecular sieve drying field for a regeneration technique capable of maintaining the P.sub.w at the 10.sup.-9 or lower level.